Processes for converting c2-c5 hydrocarbons to gasoline and diesel fuel blendstocks

ABSTRACT

Methods for the thermal olefination of a methane feedstream involving the thermal cracking of the methane feedstream at selected temperatures and pressures in the absence of a catalyst, steam or added oxygen. The methane feedstream contains greater than 85 wt % methane, and the thermal cracking produces an effluent stream containing greater than 20 wt % ethylene. Thermal cracking is optionally performed at less than 1,100° C., and in some embodiments at 850-900° C. The methane feedstream optionally contains greater than 95 wt % methane and produces an effluent stream containing greater than 30 wt % olefins. Methane in the effluent stream may be recycled to the methane feedstream.

Disclosed are processes for the conversion of C2-5 hydrocarbons to gasoline and diesel engine fuel blendstocks. C2-5 alkanes are converted to alkenes which are subsequently converted to produce targeted ranges of C₄ to C₁₆₊ fuel blendstocks. This invention offers a specialized thermal and multi-iterative chemical reaction process to transform any source comprising C₂+ light hydrocarbon streams into compounds for use as primarily gasoline blendstocks or diesel fuel blendstocks. The liquid effluent produced from the LG2F Processes can be specifically targeted by operating conditions and catalyst choices to yield any desired range of C₄ to C₁₂ gasoline compounds (i.e., high octane paraffins, olefins and aromatics) or as C₉ to C₁₆₊ high-performance middle distillate compounds (e.g. zero sulfur, high cetane, low pour point for use in ultra-low-sulfur diesel fuel).

Production of Gasoline/Diesel Fuels from CH₄

The LG2F Process can be tailored to utilize a specialized high-temperature thermal cracking process, referred to herein as methane thermal olefination (“MTO”) with light gas feedstocks comprised primarily of Methane (CH₄). Ethylene (C₂H₄) is the key product of MTO and may have viable uses as a valuable feedstock in the petrochemical marketplace (primarily to make polymers) augmenting or replacing the need for traditional ethane steam cracking and propane dehydrogenation methods.

The LG2F Process for performance of MTO is shown in Diagram 7. The MTO cracking unit is operated generally above 850-900° C. at low pressures not above 150 psig and preferably below 30 psig due to the stress on the metallurgy, without the requirements for a catalyst or steam in the reaction. The MTO reaction, depending upon the feedstream content and the process configuration, can produce high concentrations (e.g. generally 20-80+% wt.) of C₂H₄. The olefin-rich C₂H₄ produced can then be processed first by the LG2F catalytic reaction (R2) with an appropriate recycling loop for unprocessed alkanes back to C2+ Thermal Olefination process to produce any targeted range of C₄-C₁₂ gasoline blendstocks or C₉-C₂₄ diesel blendstocks. The presence of benzene (C6H6) can be condensed prior to any oligomerization step with a simple knock-out drum. Special catalytic methods may be utilized for acetylene-hydrogen rich MTO effluent streams which favor nickel-silica based zeolite catalysts that can be oligomerized in a dedicated LG2F R2 reactor. Methane and hydrogen are unreacted in the R1 and R2 LG2F process and depending upon the gas separation options chosen can either be purged for downstream uses, recycled to MTO as a feedstream (raw or merged), reused as process fuel, or reused as a diluent in the LG2F reaction sequence to create equilibrium in the process.

The process of converting methane to usable higher-molecular weight molecules is challenging due to the strength of the carbon-hydrogen bond. The MTO reaction in this invention uses an efficient thermal cracking process of methane at high temperatures without catalysts—similar to Thermal Olefination—to create an effluent comprised of C2+ alkenes which can be utilized in the LG2F process without the expense of cryogenics or multi-stage fractionation. Other unrelated methane activation techniques known to those schooled in the art may exist to convert methane to alkenes may also be employed here. However, these might involve various oxidative coupling techniques (e.g. O₂/H₂O; SOCM), nanowire methods, platinum-based catalysts, etc. which can add cost and complexity and are therefore optional but not required in this invention. The LG2F process may receive any C2-C5 alkene-rich feedstream from any source into an appropriate R2 oligomerization reaction sequence to produce premium grade fuels, value-added products, and fuel blendstocks. Methane while useful as a diluent for managing R1 and R2 reaction temperatures, is generally unreactive in the LG2F R1 and R2 process streams because it tends to only react at higher temperatures, generally above 850-900° C. and up to 2000° C.

Therefore, due to the global abundance of low-cost and widely available commercial quality feedstreams generally comprised of >85% wt. methane, the MTO reaction for producing C2+ alkenes adds a valuable methane activation feature to the LG2F process.

The basic chemistry of MTO is 2CH₄->C₂H₄+2H₂. Side reactions may also produce notable quantities of acetylene and benzene. For optimal selectivity and conversion of olefins, methane recycling back through MTO may be utilized. C2H4 is a prime olefin produced by MTO which provides the ideal feedstock to the LG2F oligomerization process by using the C₂₊ catalytic reactor (R2) as illustrated herein. Hydrogen does not react in the LG2F process and can be extracted for reuse in a variety of ways (e.g. in refining, in selective hydrogenation, industrial fuel, etc.). This MTO process operates without any requirement for O₂ or steam or water gas shift reactions in the thermal reaction. This process does not require complex multi-stage distillations or cryogenic separations. This process when augmented with LG2F produces fuel grade gasoline and diesel products without ultra-fine purity typical of petrochemical processes. Alkane byproducts from MTO do not react in the R2 catalytic reaction but C2-C5 alkanes can be recycled through the R1 thermal olefination process and methane can be recycled back to MTO to maximize yield of fuel grade blendstocks. Some variations of the MTO process may utilize specialized high-temperature catalysts including those with compounds to promote or accelerate the reaction. However, the temperature required to sustain the MTO reaction calls for frequent regeneration methods and may also limit catalyst life. Therefore, use of catalysts may be less efficient that non-catalytic high temperature MTO methods.

In one embodiment, a feedstream comprised of methane gas enters the MTO reactor at a temperature above 850 C. and operating at 1 atm. The MTO reaction has no catalyst and no steam, and it produces an effluent comprised of ethylene and hydrogen. This MTO effluent is passed through a hydrogen separation process to better isolate the ethylene and to also cleave off any unprocessed methane for potential recycling. The separated stream comprising methane can be used in alternative ways, for example as process fuel, recycled to LG2F as diluent or recycled to MTO as feed. The olefin-rich effluent now separated from methane can be processed in the R2 oligomerization reactor of the LG2F process using a zeolite catalyst or any related alkene oligomerization catalyst known to those skilled in the art to produce valued products.

In another embodiment, a feedstream comprised of methane gas enters the MTO reactor at a temperature above 850 C. and operating at 1 atm. The MTO reaction has no catalyst and no steam, and it produces an effluent comprised of acetylene, ethylene, benzene, and hydrogen. This MTO effluent is passed through a benzene liquid knock-out process to better isolate the acetylene, ethylene, hydrogen, and unprocessed methane. This remaining gas effluent is then processed in a special R2 oligomerization reactor tailored to convert C2 alkynes with hydrogen to olefins using nickel-silica catalysts or other catalytic methods known to those skilled in the art and then this is immediately followed by a partial hydrogenation step to increase the proportion of compounds in the now oligomerized MTO effluent to C4+ olefins. The output of this special oligomerization and partial hydrogenation step can then be easily separated (e.g. via membrane or molecular sieve; without expensive cryogenics or fractionation) to cleave off any unprocessed methane for potential recycling. The separated stream comprising methane can be used in alternative ways, for example as industrial process fuel, recycled to LG2F as diluent or recycled to MTO as feed. The C4+ olefin-rich effluent now separated from methane can be processed in another R2 oligomerization reactor of the LG2F process using a zeolite catalyst or any related alkene oligomerization catalyst known to those skilled in the art to produce valued products.

In another embodiment operating at similar conditions, any MTO effluent stream comprised of olefins, prior to methane separation, passes into an R2 oligomerization reactor tailored for low-activity dimerization using a Boron-impregnated zeolite catalyst or other catalytic method known to those skilled in the art thus resulting in an upgrade to the C2+ olefin molecules to an effluent comprised of C4+ olefins along with some unreacted methane and hydrogen. This dimerized olefin stream may then enter a membrane, adsorption, or molecular separation process (i.e. without any use of expensive fractionation) to separate the unreacted methane and hydrogen more easily from dimerized effluent comprised of C4+ olefin molecules. Once separated, this dimerized C4+ effluent can then be upgraded using a second R2 oligomerization reactor with an appropriate zeolite catalyst to create a spectrum of C5-C12 gasoline grade and/or C9-C20+ diesel grade fuel products and fuel blendstocks.

For those schooled in the art of catalytic alkene oligomerization reactions, any appropriate type of dimerization catalyst targeting C2+ olefins may be used generally in a low-pressure R2 reaction with the intent to limit the reaction activity and generally prevent cyclizing from occurring (thereby increasing C4+ aliphatic compounds). This may then be followed by processing any appropriate type of traditional C4+ oligomerization catalyst (e.g. specialized acid catalysts with or without zeolites, atomic-tailored molecular sieves, nickel/silica-alumina catalysts, other transition metal catalysts, bi-metallic catalysts, etc.) generally in a high-pressure R2 reaction sequence described in the LG2F process targeting a specific range of C5-C20+ longer-chain molecules including aromatics and aliphatic compounds. These isothermal reaction conditions are more fully described in the R2 oligomerization process of LG2F. (References: see Alkene Oligomerization, C. T. O'Connor, University of Cape Town, South Africa, 1990, pg. 329-348; The Changing Landscape of Hydrocarbon Feedstocks for Chemical Production: Implications for Catalysis: Proceedings of a Workshop, 2016, National Academies of Sciences, Engineering and Medicine, Joe Alper, et al., https://doi.org/10.17226/23555)

In another embodiment, a C2+ alkene-rich feedstream from any methane activation source enters the R2 dimerization reaction prior to any cryogenic or fractionation process allowing the alkenes to be dimerized with no impact on any unreacted methane. This technique allows for low-cost membrane separation methods to more easily separate the dimerized R2 effluent into two stream—one to recycle methane back to the methane activation process (e.g. MTO) and the second to either be used as C4+ olefins or processed into another R2 reaction for making fuels an fuel blendstocks.

In another embodiment, a C2+ alkene-rich feedstream from any methane activation source enters an alkane/alkene molecular separation process. This technique allows for the separation of alkanes comprised primarily of methane to be separated from the alkenes comprised primarily of ethylene. In this case, the C1+ alkane-rich stream is recycled back to the methane activation process (e.g. MTO) and the C2+ alkene-rich stream can be used as intermediate olefin products or fed into any appropriate LG2F sequence of R2 reactions for making fuels and fuel blendstocks.

In another embodiment, a feedstream comprising >90% (wt) methane enters the MTO reactor at a temperature above 850 C. and operating at 2 atm. Prior to entering the MTO reactor, the gas feedstream is processed to remove sulfur and related contaminates using methods known to those schooled in the art of processing raw natural gas. The MTO reaction has no catalyst, no steam, no chemical additives and produces an effluent comprised of >20% (wt.) ethylene. The MTO reaction operates to minimize undesirable over-reactions and minimize coking; the effluent comprises less than 2% alkynes. The MTO reactor may also operate at temperatures generally below about 1100C which thereby allows specialized alloys, chemical plating options, ceramic metallurgy (e.g. Al2O3, SiC, etc.) or thermal deposition techniques to reduce coking on the walls of the reactor tubes. The entire MTO effluent is then passed to an R2 low-pressure dimerization process to convert the C2+ olefins to C4+ olefins and thereby allow a low-cost separation technique (e.g. membrane, adsorption or molecular sieves, without fractionation or cryogenics) to cleave off the unprocessed methane for recycling back to the MTO reactor, thereby increasing the conversion efficiency of the MTO process.

In a related embodiment, the R2 dimerization process described above may involve the merging of LG2F R1 effluent from processing raw or recycled ethane (comprised of C2+ olefins) with the unseparated MTO effluent from processing raw or recycled methane (comprised of C2+ olefins). In this case, the methane will be unreacted in the R2 process, awaiting subsequent separation which is made easier by the low pressure dimerization of what were close-boiling C2/C3 olefin compounds.

In another embodiment, a feedstream comprised of high-purity methane (>95% wt.) enters the MTO reactor operating at a radiant temperature above 950 C. in the absence of any catalyst, chemical additives, steam or oxygen in the reaction, and with no sulfur, mercury, nitrogen, water or related contaminates in the feed above known industry standards for dry natural gas. The single-pass MTO reaction produces an effluent comprised of >30% wt. C2+ olefins and some unreacted methane.

In one aspect, a feedstream comprised of C1-C5 alkanes with >90% (wt.) methane gas enters the MTO reactor at a temperature above 850 C. and operating below 3 atm. The thermal reaction has no catalyst and no steam and produces an effluent comprised of ethylene and hydrogen. This MTO reaction with C2+ alkanes is prone to coking and so particular methods must be employed to prevent any obstruction to the gas flow in the reactor coil. This invention calls for the use of small alumina spheres to be used as a carbon collector device as hot gases exit the MTO reactor. The spheres (or similar shapes) stored in a carbon or stainless-steel shell tube gather carbon deposits while allowing the effluent gases to pass through the carbon collection chamber. In a related manner, another set of small alumina spheres can be periodically inserted via an automated conveyer system inside the top of the reactor coil to fall into the tube and lightly disturb the inner diameter of the coil and thereby force carbon buildup (coke deposits) to dislodge from the walls of the reactor and then fall into another collection chamber tailored for the shedding of carbon deposits from the walls of the reactor. Additional regeneration methods using diluted air typically less than about 5% oxygen may also be used to eliminate carbon build-up on the reactor walls using the 2-step regen sequence as described in the R1 Thermal Olefination process, These regeneration methods vary based upon the use of higher operating temperatures (e.g. >1000° C.) as required for MTO processing that may not allow for anti-coking plating methods as available for use in R1 Thermal Olefination and also based upon the composition of the MTO feedstream that may include excess C2+ hydrocarbons which tend to generate high levels of carbon deposits.

Alkene Feedstocks

The LG2F Process is also useful with light alkene gases, including ethylene, propylene, butylene and iso-butylene. Typical Cat-Cracked Gasoline byproducts include C₃ alkenes and LPG which are desirable feedstocks to the LG2F process for upgrading to higher value gasoline or diesel fuel blendstocks. The presence of alkenes in the feedstock may favor the use first of the acid-catalyzed chemical reaction, as exemplified in Diagram 8.

As an illustration of the processing of alkene gases, a single pass yield of the C₂₊ acid-based chemical reaction, shown below in Diagram 9, is from a C₃ olefin feedstock and demonstrates the production of gasoline grade compounds. This reaction was made at 45 psig and 3 WHSV across a range of temperatures. As illustrated, the aromatic hydrocarbon content (A₆₊) varied by the reaction temperature which can be used to increase octane values of gasoline blendstocks.

Diagram 9—Chemical Reaction Selectivity of Gasoline Hydrocarbons by Temperature

Another embodiment of this LG2F invention, shown in Diagram 10, receives the byproduct light gases from the catalytic cracking process (often containing C₃₊ olefinic compounds, e.g. propylene) to produce gasoline range blendstocks. In this embodiment, the olefinic feed bypasses the thermal olefination reactor and goes straight into the multi-iterative acid-catalyzed reaction in a single or multi-bed reactor configuration with a recycle loop. This process is designed to provide excess hydrogen to yield C₆ to C₁₁ range gasoline compounds (i.e. paraffins, olefins and aromatics) for use with other gasoline blendstocks. All gasoline products in this embodiment are very-low benzene, sulfur-free and nitrogen-free. A byproduct of this process is unused hydrogen.

Another embodiment of this LG2F invention receives the byproduct light gases from the catalytic cracking process (often containing C₃₊ olefinic compounds, e.g. propylene) to produce diesel range fuel blendstocks. This embodiment bypasses the initial thermal olefination and goes straight into the multi-iterative acid-catalyzed reaction in a single or multi-bed reactor configuration with an R2 catalyst tailored for the feedstream before re-entering the LG2F recycle loop. This process is designed to provide excess hydrogen and to yield any specified range of C₄ to C₁₂ gasoline blendstocks or C₉ to C₂₄ middle distillate for use as diesel fuel blendstocks. A byproduct of this process is unused hydrogen.

The foregoing processes are examples of a range of processes using alkene feeds, further including the following:

-   -   C₂+ alkene gas streams exiting the catalytic cracking unit are         transformed to C₆+ gasoline constituents first via LG2F chemical         reaction (R2), followed by a recycle loop that restarts thermal         olefination and a chemical reaction loop resulting in higher         liquid gasoline yields;     -   C₂₊ light hydrocarbon streams with primarily olefinic compounds         are merged to increase the available volume of light gas         compounds for conversion via R2 processing with recycle loops to         R1+R2 to produce gasoline blendstocks using the LG2F process;     -   C₂₊ light hydrocarbon streams with primarily olefinic compounds         are merged to increase the available volume of light gas         compounds for conversion to light gas oil or diesel fuel         blendstocks using LG2F.

Reducing Benzene

Another major feature of this light gas transformation to transportation fuel is the selective reduction of benzene, which makes the resulting products excellent for gasoline blending due to low specification limits placed on benzene for use in fuels. In the case where there is an unwanted surplus of benzene-rich C6+ aromatics extracted by liquid-vapor knockout from the R1 thermal olefination effluent, an added feature of LG2F is to combine light alkene compounds (e.g. C2-C3) from the R1 reaction with the surplus C6+ aromatic compounds into a simple low-temperature acid-catalyzed reaction to create alkyl-benzenes. See Diagram 11. This processing will convert benzene via electrophilic substitution to become productive gasoline grade blendstocks that adhere to existing limitations in gasoline specifications for high-octane aromatic compounds. This process may utilize aluminum chloride and hydrogen chloride catalysts. This process will further increase the value of the gasoline hlendstock.

Dewaxing

Another aspect of this invention is a simplified method to dewax paraffinic compounds from C₁₄ to C₄₀ hydrocarbon streams using a single-stage, low-severity, acid-catalyzed reaction process to both hydrocrack and hydrotreat middle-to-heavy grade distillate feedstocks to produce a higher-value, higher-grade middle distillate with higher fuel performance properties.

Catalytic dewaxing is typically referred to as a process that selectively removes C₁₄₊ paraffinic compounds from middle- to heavy-distillate hydrocarbon streams. This technology is usually applied to hydrocarbons used in diesel fuel and heating oils to improve its physical properties including cloud point, pour point and cold flowability. Increasing quality reduces the need of using fuel additives to improve properties and allows for more detailed control of blending specifications. The primary alternative technology to catalytic dewaxing is solvent based dewaxing which applies a solvent extraction method to heavy paraffinic compounds that preserves the chemical structure.

Configurations of traditional dewaxing units vary but are most often categorized in two categories: a single or dual bed reactor. The choice in configuration depends on preference for hydrotreating integration into the dewaxing catalytic system. The inlet streams have higher concentrations of sulfur and nitrogen which will deactivate noble metal catalysts. So, a hydrotreating bed is typically integrated before the dewaxing catalyst to ensure minimal degradation of performance.

Traditional Dewaxing Methods

Traditional refinery dewaxing catalysts are nickel- or platinum-based selective zeolites, which is a molecular sieve catalyst. By controlling pore size, these methods control the types of molecules that enter the catalytically active sites. Specifically, the pore sizes are set to allow n-paraffinic compounds but not isoparaffinic compounds (0.6 nm). Traditional hydrotreating catalysts commonly use Ni/Mo metal combination to perform the hydrogenation of nitrogen and sulfur-based compounds. The configuration of these catalyst depends on the level of protection needed in a dewaxing unit. If there are lower than normal catalyst poisons, then a single reactor can be used with a protective bed above the dewaxing bed. However, if poisons are an issue then a separate hydrotreating bed will be beneficial to sustained catalyst life. A comparison between typical single and dual bed catalysts are show below.

Traditional methods for dewaxing require a separation between two catalytic beds with one performing hydrotreating and the other selectively cracking n-paraffinic compounds. Noble metal catalysts propose too high of a risk for poisoning from hydrogen sulfide and ammonia, hence the removal of these gases before dewaxing. However, base metal catalysts lack the activity needed to dewax a hydrocarbon stream effectively and require larger utility costs.

This invention utilizes a unique, low-severity method for hydrocracking the C¹⁴⁻ to C₄₀₊ paraffins or any targeted range of n-paraffins compounds using a specialized zeolite catalyst with the capability to simultaneously hydrotreat the feedstream thereby removing the sulfur and nitrogen-based compounds and cracking the low-melting paraffins in a single step process. This unique method reduces total costs of processing and eliminates the need for additives used in the field. The main target is cracking broad scope n-paraffinic compounds since even n-tetradecane (C₁₄) melts above low ambient temperatures. Having even a single branch significantly reduces the melting point by ˜80 F. while still having a cetane value of 67.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes, equivalents, and modifications that come within the spirit of the inventions defined by following claims are desired to be protected. 

1. (canceled)
 2. A method for methane thermal olefination comprising thermal cracking a methane feedstream comprising more than 85 wt % methane at a temperature of less than 1,100° C. and a pressure of at most 150 psig, the thermal cracking being performed without a catalyst and without steam to yield an effluent stream containing greater than 20 wt % ethylene.
 3. The method of claim 2 in which methane in the effluent stream is recycled to the feedstream for the thermal cracking.
 4. The method of claim 2 in which the thermal cracking is performed without added oxygen.
 5. The method of claim 2 in which the methane feedstream comprises more than 95 wt % methane feedstream and the effluent stream contains greater than 30 wt % olefins.
 6. The method of claim 2 in which the thermal cracking is performed at 850-900° C.
 7. The method of claim 2 in which the effluent stream is passed through a hydrogen separator to separate the ethylene from hydrogen and methane in the effluent stream.
 8. The method of claim 7 in which the separated methane is recycled to the feedstream for the thermal cracking.
 9. The method of claim 2 in which the thermal cracking is performed at 50° C. and 1 atmosphere pressure yielding an effluent stream comprising hydrogen, methane, benzene and acetylene.
 10. The method of claim 2 in which alumina is provided during thermal cracking to remove carbon. 